1. Field of the Invention:
The present invention relates to an objective lens system which is employable in an ultraviolet region, particularly in a far ultraviolet region with wavelengths of less than 300 nm. The system can be used within a microscope.
2. Description of the Prior Art:
Most conventional objective lenses for use within microscopes are employable in visible and infrared regions but cannot be used in ultraviolet and far ultraviolet regions. This is because most optical glass materials do not transmit shorter-wavelength rays, i.e., rays whose wavelengths are shorter than 300 nm, i.e., ultraviolet and far ultraviolet rays.
Assuming the numerical aperture (NA) of an objective lens of a microscope remains constant, its resolution limit is increased as the wavelength is shortened. Therefore, it is possible to observe a sample in greater detail by shortening the wavelength of illuminating and observed rays. Further, a greater variety of samples fluoresce when exposed to ultraviolet rays (compared to those which fluoresce when exposed to visible rays). Therefore, to obtain more information by observing a sample through a microscope, it is advantageous to use light in the ultraviolet region. To this end, an objective lens which is employable in the ultraviolet and far ultraviolet regions is required. The following prior art objective lenses have generally been employed.